Frame grid and method of fabrication



June 15, 1965 e.. sAMuELs 3,189,779

FRAME GRID AND METHODOF FABRICATION Filed 001;. 31, 1950 I 2' Sheets-Sheet 1 June 15, 1965 G. sAMUELs FRAME GRID AND METHOD OF FABRICATION 21 Sheets-Sheet 2 Filed Oct. 3l. 1960 INVENToR. Gerard Samuets BY WM i United States Patent O 3,189,779 FRAME GMD AND METHOD OF FABRICATION Gerard Samuels, Teaneclr, NJ., assigner to Radio Corporation of America, a corporation of Deiaware Filed er. :311, 1964.), Ser. No. 66,226 6 Claims. (Cl. 313-350) This invention relates to electron discharge tubes and more particularly to a frame grid and its method of fabrication.

It is well known that an ideal or theoretically perfect grid for an electron discharge tube would be a Mare well grid, that is, a grid having an infinite number of equally spaced lateral wires of innitesimal diameter. Use of such a grid would result in an electron tube of optimum electrical performance, having such desired characteristics as high transconductance and perfectly linear and hence distortionless output. Although a true Maxwell grid has not yet been made, approximations thereto may be achieved by fabricating grids having a great many closely and uniformly spaced lateral wires of very small diameter. Modern practice is such that in the attempt to closely approximate such Maxwell grids, the diameter of the grid lateral wires in the grids of certain types of tubes has been reduced to the point where the wires are not self-supporting when wound in conventional form about unsupported side members, but must be wound on support frames.

Two types of support frames are presently employed in the art. The iirst type is a multi-piece frame composed of a pair of parallel side members about which the lateral Wire is wound, with cross straps extending between and adjacent each end of the side -members for bracing them in spaced apart relation. The second type is a single-piece frame punched and formed from a flat stock of sheet metal. The main Vdiifererice between grids made from the two types of frames is that grids utilizing the former type of frame are tubular grids, having lateral Wires on each side of the frame, whereas grids utilizing the later are generally flat grids having laterals on one sidevonly. Because of this difference, different methods are generally employed in the fabrication of the two grid types. This invention is related to the former or multi-piece type of frame.

Heretofore, grid laterals have been secured to their support frames in man? ways, the more common of which include a fused metal joint, produced by brazing or welding, a cemented joint, or a mechanically secured joint obtained through the practice of notching the support frame, laying the lateral wire in the notch, and swaging the walls of the lnotch closed over the lateral wire. Moreover, conventional practice has been to secure each lateral wire turn (that is, lateral) of the grid to the grid to the grid support frame. In many instances, however, where the lateral wire is very small and fragile, only the end turns of a continuous helical winding wound about the frame are secured thereto.

Notcln'ng and swaging, for example, have not proven practical for securing all the lateral Wire turns of an extremely fine wire, small pitch winding to a support frame because of the difticulty of providing notches in the support frames which are small enough to permit close lateral wire spacing, or which can be spaced accurately and uniformly along the length of the frames. Although notching and swaging has been employed to secure only the end turns to a lateral wire frame, this method has the disadvantage that the pressure exerted on the support frame by the notching and swaging tools tends to warp or distort the frame.

Welded joints between all the lateral wire turns, or even only the end turns and a support frame have also been found diicult to produce with very fine wire. This 3,139,779 Patented .lune 15, i965 is because of the diiiculty of providing uniform Icontact between the weld electrodes and each of the wire turns. This slightest excess in weld pressure against the fragile wires results in burned and severed laterals, and insufficient pressure results in faulty joints and loose laterals.

The method of brazing lateral wires to support frames has the disadvantage that the brazing process is generally accomplished at elevated temperatures. Since the lateral wires are usually of one material and the support frames of another, the support frame material having the larger thermal coefficient of expansion, there is an expansion differential tending to stretch the lateral wires and distort the support frames during the brazing process. Because of the greater strength of the support frames, as compared to that of the laterals, the latter are likely to be stretched beyond their elastic limit which results in loose laterals or reduced tension in the laterals when the grid is cooled. Such reduction in the tension of the laterals :makes the grid more susceptible to undesirable vibrations and the production of microphonic noise, as is generally understood.

Attempts to avoid the problems incident to high temperature brazing have resulted in the development of low temperature cementing techniques, using glass frit and the like. Even at the relatively low temperatures required to set these cements, however, some inelastic stretching and reduction in tension of the lateral wires occur. Moreover, grid fabrication by cementing is a relatively expensive process. That is, in the manufacture of grids, it has been found most expeditious .to Wind a continuous lateral wire helix over the entire length of a grid, and then to remove some turns from each end thereof to provide turnless lengths, or legs, which are utilized to assemble the grids within electron tube mount assemblies. lf all the turns are cemented to the support members, a separate operation is required to sever each of the end turns frou the grid legs. Conversely, if only predeterdined turns are cemented to the support members, special masking procedures must be employed to permit the application of the cementing material to only the desired portions of the grid. In either event, extra operations on the grid assemblies are required which increase the costs thereof.

Accordingly, it is an object of this invention to provide an improved frame grid assembly and a method of its fabrication wherein the fabrication problems of the priorart frame grids are avoided.

More particularly, it is an object of this invention to provide an improved frame grid assembly and a novel method of its assembly whereby the end turns of a continuous lateral wire wound about a support frame are securely fastened to the grid frame.

Another object of this invention is to provide an improved method of fabrication of frame grids whereby distortion or stretching of the lateral wires beyond their elastic limit is avoided, and whereby the lateral Wires may be accurately spaced on the grid frame.

These objects are realized in accordance with this i-nvention, by the construction of a support frame about which a very iine continuous wire is wound. The frame comprise a pair of parallel side members provided with bridging or cross straps adjacent opposite ends thereof for accurately and rigidly spacing the side members apart. The cross straps are securely iixed to the ends of the side members, as by brazing or welding, and in accordance with this invention, at least one strap at each end of the support frame is provided with a free end which extends beyond one of the side members.

A feature of this invention relates to the method of securing the ends of the winding to the support frame.

Prior to the winding of the laterial wire about the frame, an end of the lateral wire is positioned, by means herein after described, along a portion of a side member at the intersection of a cross strap free end and the side member. Thereafter, the free end of the strap is bent or wrapped around the side member, the wire end being tightly sandwiched and permanently clamped therebetween.

Having thus secured the end of the lateral wire to the support frame, the Wire is then Wound under tension about the frame over the longitudinal expanse between the straps at opposite ends thereof. After the winding is completed, the end of the last turn of the winding is disposed along the side member adjacent the free end of a cross strap at the other end of the frame, and the strap end is bent over against the side member. Both ends of the lateral wire are thus securely clamped between the cross straps and the side member, and the wire extending from the Wound frame to the winding means may then be broken off to complete the grid assembly.

This arrangement provides an eilicient assembly wherein the grid laterals may be wound at any desired pitch, and wherein the winding is rigidly secured at opposite ends of the support frame. Also, since the winding is secured to the frame without the application of any heat, the original winding tension and hence the uniform spacing of the lateral wire turns .in maintained. Furthermore, the force required to clamp the strap ends against the side members is relatively small, thereby causing substantially no distortion of the support frame.

These and other features and advantages of the invention will be more clearly set forth in the following detailed embodiment of the invention described in connection with the accompanying drawing in which:

FIG. 1 is a view in perspective showing a grid frame of the type which may be employed in the practice of this invention;

FIG. 2 is a view in perspective of an apparatus which may be employed to fabricate frame grids in accordance with this invention;

FIG. 3 is an end View of a portion of the apparatus shown in FIG. 2, but shown at a later step in the grid fabricating cycle;

FIG. 4 is a plan view of the same portion of the apparatus as shown in FIG. 3, but at a step in the grid fabricating cycle later than that illustrated in FIG. 3;

FIG. 5 is a View of a detail of the apparatus shown in FIG. 2, but at a still later step in the grid fabricating cycle than that illustrated in the view of FIG. 4; and,

FIG., 6 `is a view in perspective of a frame grid assembly made in accordance with this invention.

FIG. 1 shows a grid frame 10 of the type which may be employed in the practice of this invention. The frame comprises a pair of parallel, cylindrical side or upright members, or supports 11, having end lengths or legs 16 and 17. Two pairs of parallel cross straps 18 and 20 extend between the side members or side rods 11 adjacent each end thereof and are joined in substantially line contac't to the side members 11. Further, all the cross straps have free ends 22 and 23 which extend beyond side members 11. Since one purpose of the cross straps is to support the side members in accurate spaced apart relation, the straps are of rigid material, and are securely fastened to the side members. Moreover, to permit fastening of the ends of the lateral wire to the grid frame, as will be described hereinafter, the straps should be of relatively non-resilient material. In this embodiment, the cross straps are made of annealed molybdenum and are welded to the side members 11.

An apparatus which may be employed for fabricating grids made according to this invention is shown in FIG. 2, and includes a base plate 39 for supporting the lateral wire feed mechanisms to be described, and a mandrel 32 for receiving a frame 1t?. The thickness of mandrel 32 is less than the diameter of the side members 11 and the distance between `the lateral wire turn planes on each side of the frame is determined entirely by the diameter of the side members. Since the lateral wires do not contact the mandrel, the lateral wires are not dragged or distorted upon removal of the wound grid from the mandrel.

Mandrel 32 is mounted within a chuck 33 fixed on the end of shaft 34; the shaft being mounted for simple rotary movement as in bearings 35 on the side of a gear box 37. Within gear box 37, shaft 34 is geared to shafts 40 and 42, either of which may be used to rotate mandrel 32.

Shaft 42 is coupled directly to they armature'of an indexing motor 46, while shaft 4% is coupled to a known driving system (not shown) adapted to rotate mandrel 32 alongwith the armature of the indexing motor 46. The driving system is also coupled to lead screw 47 for feeding the winding mechanisms parallel to and in synchronization with the rotation of mandrel 32 for providing the desired pitch of the wound wire turns over the length of the frame 1Q. Known electromechanical clutch means are also provided (not shown) for simultaneously coupling or decoupling the driving system from shaft 40 and lead screw 47. The effect of this clutch arrangement is that mandrel 32, shaft 42, and the winding mechanisms are all driven by the driving system while the clutch. means are engaged, while indexing motor 46 may rotate mandrel 32 independently of the driving system and the winding mechanisms while the clutch means are disengaged.

|The driving system and clutch mechanisms mentioned are known in the art, and for the sake of brevity and clarity, further description thereof will be omitted.

Indexing motor 46 may comprise a commercially available motor of the type which has the feature that upon receipt of a first electrical current signal, the motor armature will index from any angular setting it happens to be in to a iirst predetermined angular orientation. Upon receipt of another signal, the/'armature will rotate from the first predetermined orientation through a discrete angular increment. In the apparatus shown, the indexing motor 46 is so adjusted to rotate the mandrel 32 to an angle 45 from the vertical upon receipt of a first signal, as shown in FIG. 3, and to a vertical position upon receipt of a second signal, as shown in FIGS. 2 and 5. Further signals repeat the cycle.

The winding mechanisms mounted on base plate 30 comprise a wire guide 55 mounted on a movable carriage or slide 57. A table 59 on base 30 supports the carriage 57, and a spool 61 of iine lateral wire 63 is rotatably mounted on a shaft 65 supported on table 59. Friction brake 67 engages spool 61 and maintains wire 63 at a desired amount of tension during the winding operation.

For reasons which will become clear hereinafter, the wire guide 55 is arranged so that it may be moved laterally with respect to mandrel 32 in a series of discrete steps in addition to the feed of the winding mechanisms as provided by the driving system.

For accomplishing this stepping motion, carriage 57 is slidably mounted on guides 7i? supported by block '71 mounted on table 59. These guides are parallel to man drel 32. A face cam 72 having a development in the form of a series of raised and depressed rounded steps '74 is provided adjacent one end of carriage 57. The cam is in engagement with a rod cam follower 76 extending from the carriage 57. Compression springs 77 are provided on guides between the carriage S7 and block 71 which oppose the forward motion of carriage 57 thereby maintaining cam follower 76 in Contact with cam 72. Cam 72 is mounted on a shaft driven by an electrically actuated step motor 78 mounted on table 59, and rotation of cam 72 causes carriage 57 to index forward or backward through a series of steps equal in length to the height of the cam steps.

Included in the apparatus shown in FIG.. 2 are a pair of jaws 79 for holding an end of wire 63 at the start of the grid fabricating process. For reasons to be described, jaws 79 are mounted at the end of the plunger 8b of a fast acting solenoid 81. Also shown are a pair of crimping tools 82 and 83 adapted for bending over the cross strap free-ends 22 and 23 against the support members 11. Crimping tools 82 and 83 are mounted on the plungers of solenoids S4 and 85.

Indexing motor 46, the step motor 7d, the electromechanical clutch means, and solenoids Sl, 34 and 85 are actuated by electrical currents, and proper timing for these devices may be conveniently achieved through the use of simple cam-microswitch arrangements (not shown), the cams being synchronously driven by a clock motor.

The fabrication of grids made according to this invention will now be described.

A grid frame 10 is mounted on mandrel 32 and positioned thereon such that the posts 87 are adjacent the legs 16 of the frame. A rst end of the wire 63 from spool 61 is threaded between the posts 87 of the wire guide 55, passed over a frame side member 1l, and secured within jaws 79, wire 63 being under some initial tension to maintain it snugly against side member 11, as shown in FIG. 2.

The apparatus is energized, and with the driving system disengaged, an electrical signal is applied to the indexing motor 46. The purpose of this motor will now become clear. As described, the armature of indexing motor 46 rotates mandrel 32 45 with respect to the vertical upon receipt of a first electrical signal to the position shown in FIG. 3. Then, as cam 72 is rotated by the step motor to index carriage 57 and wire guide 55 forward through one step, wire 63 is threaded along the side member 11 between the strap ends 22 and 23 as shown in FIG. 4.

A second electrical signal is then applied to the indexing motor 46, and the mandrel is rotated to a vertical position. Crimping tool 82 is then actuated downwardly against the strap ends 22 and 23, thus bending the strap ends against the frame side member 11 with wire 63 sandwiched therebetween (FIG. 5). The strap ends are bent and stretched beyond their elastic limit, thus securely and permanently clamping the end of wire 63 between the strap ends and the edge of the frame ltl. Solenoid Si is energized, and the rapid motion of plunger 80 into the solenoid snaps off the extending end of wire 63 against the cross strap edges on the side toward the jaws 79.

Having thus aiixed the first end of wire 63 to the frame 10, the driving system is engaged through the clutch means to rotate mandrel 32 and to advance table 59 and carriage 57 and wire guid-e 55 mounted thereon along the length of frame 10.

Mandrel 32 is rotated through a number of turns suflicient to wind wire 63 about the side members 11 over the expanse of the frame 10 between the strap pairs f3 and 2Q. At the end of the winding operation, the driving system is disengaged and mandrel 32 cornes quickly to a halt due to the friction of the parts within gear box 37. An electrical signal is applied to the indexing motor 46, and as at the start of the fabricating operation, mandrel 32 is rotated to a position 45 to the vertical, Wire 63 is threaded through the extending ends 22 and 23 of strap pair Ztl, and the strap ends 22 and 23 are subsequently wrapped around a side member 11 by the crimping tool 83 to secure the end of wire 63 to the support frame 10.

Cam 72 is indexed, and cam follower 76 engages a depressed step 74 on cam 72. Carriage 57 is indexed abruptly backwards by the action of compression spring 77 and the extending portion of wire 63 from the frame 10 to the wire guide 55 is broken off against the cross strap edges to complete the grid assembly.

No further fabricating steps are required since the tension under which the lateral wire turns are wound serve to maintain the grid turns in place along the frame, while the locking of the wire ends to the frame, as described, is a positive and permanent means to maintain the wire under tension thereinafter. Moreover, since the extending ends of the lateral wire are broken olf at the cross straps, as described, no additional operations are required to remove turns or lateral wire tails from the grid legs.

After the completed grid electrode is removed from mandrel 32, table 59 is indexed back to its original position in preparation for the winding of a new grid frame. In one embodiment of the apparatus described for fabricating grids according to this invention, means are provided for indexing jaws 79' over mandrel 32 to wire guide 55' for automatically picking-up the starting end of wire 63 and advancing it over mandrel 32 and a frame thereon. Means are also provided for automatically loading and unloading the grid frames and completed electrodes `from mandrel 32. By use of such apparatus, the grid electrodes of this invention have been fabricated rapidly and economically.

What is claimed is:

l. A v'grid for an electron discharge tube, said grid comprising a pair of spaced support members, a plurality of spacer members extending between said support members and having portions affixed .to said support members, said spacer mem-bers having end leng-ths beyond said portions disposed partially around and in tightly clamped relation with surface portions of said support members, and a ywire wound about said support members, the ends of said wire extending between said end lengths and said surface portions and being secured :to said support members thereby.

2. A frame type grid electrode comprising a pair of side rods, bracing straps extending between said side rods adjacent to the ends thereof, said straps having end por-tions disposed partially around and in tightly clamped 4relation with surface portions of said side rods, and a helical winding of line wire wound around said side rods, the ends of said wire .being disposed between said strap end portions and said side rod surface portions and being secured to said side rods thereby.

y3. A frame type grid electrode comprising a pair of side rods in parallel relation, pairs of parallel bracing straps joined to and extending between said side rods adjacent to the ends of said side rods and transverse thereto, at least one of each of said pair of straps having a curved end length extending around a surface port-ion of said side rods in tightly clamped relation therewith, and a helical winding of ne wire embracing said side rods, the ends lof said wire extending between said curved end lengths and said surface portions and being secured to said side rods thereby.

4. A frame type grid electrode comprising a pair of side rods in parallel relation, pairs of parallel cross straps extending between said side r-ods adjacent to the ends of said side rods and transverse thereto, said straps having inner surfaces joined to said side rods and curved end lengths extending around `surface portions of said side rods and in tight engagement therewith, and a helical winding of tine wire embracing said side rods and extending over the area between said pairs -of straps, Ithe ends of said winding being disposed between said curved end lengths and said side rods and being secured to said side rods thereby.

5. A frame type grid elect-rode comprising a pair of cylindrical side rods in parallel relation, pairs of parallel and oppositely disposed bracing straps extending between said side rods adjacent to the ends of said side rods and transverse thereto, said straps having inner surfaces adjacent to the ends of said straps joined to said side rods, and having curved end lengths disposed partially around and in vtightly clamped engagement with surface portions of said side rods, and a helical winding of ne wire embracing said side rods, the ends of said wire being secu-red :to said side rods by being disposed between said end lengths and said surface portions of said side rods.

6. A frame type grid electrode comprising a pair of side rods in parallel relation, pairs of parallel and oppositely disposed rigid, relatively non-resilient, bracing straps extending between said side rods adjacent opposite ends of said rods and transverse thereto, said straps together having a U-shape, :the bight of said U being formed by adjacent ends of said straps extending towards one another and in close abutment with said side rods, and a helical winding of fine Wire embracing said rods and extending over the area between said pairs of straps, each end of said wire being ldisposed between said bight of said U and said side rod and being secured to said side rods thereby.

References Cited by the Examiner UNETED STATES PATENTS 2,624,106 1/53 Foulkes 29-25.14 2,845,691 8/58 Atherton et al 29-25.l7 2,878,549 3/59 Willner 29-25.14 2,897,395 7/59 Niiiler 313-350 2,945,152 7/69 Marr; 313-350 2,960,621 11/60 Lane et al. 313-350 3,013,176 12/6l Field 313-350 3,054,430 9/62 Van Tol et al.

GEORGE N. VJESTBY, Primary Examiner.

RALPH G. NESON, ARTHUR GAUSS, Examiners. 

1. A GRID FOR AN ELECTRON DISCHARGE TUBE, SAID GRID COMPRISING A PAIR OF SPACED SUPPORT MEMBERS, A PLURALITY OF SPACER MEMBERS EXTENDING BETWEEN SAID SUPPORT MEMBERS AND HAVING PORTIONS AFFIXED TO SAID SUPPORT MEMBERS, SAID SPACER MEMBERS HAVING END LENGTHS BEYOND SAID PORTIONS DISPOSED PARTIALLY AROUND AND IN TIGHTLY CLAMPED RELATION WITH SURFACE PORTIONS OF SAID SUPPORT MEMBERS, AND A WIRE WOUND ABOUT SAID SUPPORT MEMBERS, THE ENDS OF SAID WIRE EXTENDING BETWEEN SAID END LENGTHS AND SAID SURFACE PORTIONS AND BEING SECURED TO SAID SUPPORT MEMBERS THEREBY. 